The 7th gen was very obviously a hugely different market from the 8th, hence the Wii dominating the competition yet the Wii U getting steamrolled. 

It's not a coincidence that of the three 8th gen consoles, the one that's performing the worst by far is the one dominated by family friendly cartoon titles.

Wii U already had plenty of platformers, what it needed was a little diversity in its exclusive lineup and image, something Retro were well positioned to provide.

Correlation vs causation

the Wii U is not failing because of lack of dark, gritty games. We have 30+ years of data that shows cartoony & family-friendly titles are far more popular than dark, gritty titles on Nintendo platforms.

Call of Duty, Assassin's Creed, Mass Effect, Tekken, Injustice, Ninja Gaiden, Resident Evil, Sniper Elite, Batman, Walking Dead, Bayonetta, Fatal Frame, Xenoblade, Watch Dogs, Deus Ex, Monster Hunter are all on Wii U, why has Tropical Freeze outsold each and every one of them? Why have 3rd parties stopped releasing these types of games on Wii U yet they still release cartoony & family-friendly games for Wii U?

30 years of data from a different era when the market was less dominated by 14-40 year old males than it is today. The days were you can propel a console to success on a primarily E-rated library are over. Your average consumer today is no longer the parent buying for their kids that Nintendo targets, its teenagers and guys in their 20s and 30s buying for themselves, and they would rather play T or M rated games.

Those games you list mostly had superior versions available on consoles that people already owned.

The thing is, nobody who didn't already have a Wii U was going to buy one for Tropical Freeze. It was yet another cartoon platformer on a system that already had plenty. It did nothing to address Wii U's lack of appeal to the 14-40 male crowd.

Because 2D platformers typically sell well on Nintendo platforms but they don't sell consoles.  In today's market, they're the type of games people decide to buy after they've bought a console, not because of them.  A lot of it also has to do with the over-saturation of them by indie developers.

But even then, is that even something to be proud of?  That 3rd parties only want to sell cartoony & family-friendly games on the Wii U because they recognize that those are the only types of games that sell well there?  That's kind of depressing to me because it shows to me that developers and publishers see the Wii U as a niche platform with little variety.  It also does a lot to explain why it's selling so badly and why Nintendo continues to lose market share (outside of the 7th gen).

I'm going to sound like a broken record but it still would have sold more Wii U consoles than Tropical Freeze.  Not because I think a lot of Metroid Prime but because I think so little of the console selling power of kid-friendly 2D side-scrolling platformers (outside of Mario Maker).

suck the sales, although i love metroid, id choose a DKC game.
DKCTF is my favorite wii U game, and the 3 DKC are my favorite games on snes.
just keep the DKCTF quality is what I expect from retro, and my respect from them will remain at top levels.

Who said anything about being proud? Im simply stating that the types of games that move Nintendo hardware and the ones that move PS/XB hardware are not the same. Nintendo focusing on the type of games that people buy PS/XB for is not going to help them, they will just be seen as copy-cat and still get labeled as being "kiddy".

When has Metroid ever sold consoles? Never.

 You clearly don't remember the SNES days. All three Donkey Country games sold really well and to rave reviews. It was Donkey Kong 64 that killed the franchise. It was essentially a Banjo Kazooie rip off.

Well, then they're going to continue to lose market share because they lost a lot of the casual market and the adolescent audience to smartphones and tablets.  And I never said anything about Nintendo focusing on the 18-35 adult male market.  I'd rather Nintendo diversify more by adding teens to their target demographics instead of throwing all of their eggs into two declining demographics within the console/handheld market.  Hell, I don't want them to target adult males either because NOA will end up buthering those games during the localization process.

You can criticize the Metroid series all you want but I still think a HD Metroid Prime would have moved more consoles than 'kid-friendly 2D side-scrolling platformer' #24.  At this point it's just a difference of opinion.